A ray falls on a prism $\mathrm{ABC}$ $(\mathrm{AB} = \mathrm{BC})$ and travels as shown figure. The minimum refractive index of the prism material should be

 

A point object $O$ is placed in front of a glass rod having a spherical end of the radius of curvature $30 \mathrm{cm}$. The image would be formed be

A spherical surface of radius of curvature $R$ separates air (refractive index $1.0$) from glass (refractive index $1.5$). The centre of curvature is in the glass. A point-object P placed in air is found to have a real image $Q$ in the glass. The line $PQ$ cuts the surface at a point $O$ and $PO=OQ$. The distance $PO$ is equal to: